Metal purification



Dec. 23, 1941.

H. N. GILBERT MI ZTAL PURIFICATION Filed July 26, 1940 FIG.

INVENTOR. HG HARVEY N. GILBERT.

A TTORNEY tube.

Patented Dec. 23, 1941 METAL PURIFICATION Harvey N. Gilbert, Niagara Falls, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July 26, 1940, Serial No. 347,743

Claims.

This invention relates to the treatment of metals, particularly to treatment of molten metals by the introduction of another metal such as an alkali metal.

The alkali metals, particularly sodium and potassium, are useful reagents in many metallurgical processes because of their reactivity toward oxygen and other impurities. The usefulness of these metals for this purpose has been limited in the past by the lack of a practical metals into metals which it is desired to treat.

One of these methods consists in placing the solid alkali metal in a metal cage which is then submerged in the molten metal undergoing treatment. This method is dangerous, difficult to control, and generally unsatisfactory. The metal to be treated freezes around the cage, forming a shell which subsequently bursts from vaporization of the alkali metal conta ed within it, sometimes causing an explosion a d loss of metal.

Another prior art method consists in introducing a molten alkali metal into the body of the metal to be treated, by means of a capillary This procedure is also hazardous since heat is conducted through the walls of the capillary tube, causing vapor formation in the tube with the development of high-back pressure. Furthermore, the size of the capillary must be carefully controlled to avoid introduction of large amounts of alkali metal. The prior art suggests additional methods for solving this problem but none of these has proved satisfactory.

It is an object of this invention to provide a method and apparatus for the treatment of molten metals with other metals and particularly with alkali metals. It is a further object of this invention to provide a method and apparatus .,for the introduction of alkali metals into molten metals which avoids danger of explosion or loss of the metal. Other objects will be apparent from the ensuing description of my invention.

The. above objects are accomplished in accordance with my invention by contacting a molten metal, the melting point of which is higher than the boiling point of the alkali metals,

with an alkali metal in order to vaporize said alkali metal, and confining said alkali metal vapors so that said vapors are introduced into the body of the molten metal to. be treated. By this mode of operation, the alkali metal vapors, so generated and so confined, are passed into and through the molten metal being treated and rapid and efdcient purification is obtained.

The apparatus which has been found most suitable for the practice of my process consists of a bell partially submerged in molten metal. The lower edge of the bell provides a large area of contact between alkali metal vapo'rs and the molten metal. The upper part of the bell contains means to admit alkali metal and, in the preferred form, means are provided for applying a slight pressure of inert gas to overcome the back pressure of alkali metal vapor and thus facilitate passage of vapor under the edge of the l is a container for molten metal to be treated.

2 ina bell type vesseLwith an open bottom, constructed of graphite or other suitable material. A metal plate 3 serves as the top of the bell 2. 4 is a metal inlet tube ending in an orifice by means of which the rate of flow of alkali metal into hell 2 is controlled. This inlet tube is equipped with a valve 5 which may be opened to admit molten alkali metal from a container (not shown).

Figure II illustrates amodification in which the bell is extended vertically so as to provide a reflux'for the vapors of alkali metal. This form of apparatus also illustrates a preferred means of applying pressure to the system to balance any back pressure of alkali metal vapor within the bell. In Figure 11 like reference numbers refer to similar elements. 6 is a gas inlet pipe opened to an alkali metal container 8 and. bell 2'. l is a plug which serves as a closure for container 8.-

one method of carrying out the process of my invention may be described by reference to Figure II. Molten alkali metal is charged into container 8. The bell 2' is lowered vertically into the molten metal to be treated until the bottom of the-bell is submerged. Alkali metal is then admitted through the orifice of inlet tube 4' by opening valve 5'. On striking the surface of the molten metal in container l' the alkali metal is vapbrized. The vapors pass under the edge of bell 2" and react with the impurities of the metal undergoing treatment. A slight pressure of nitrogen or other inert gas may be applied at the inlet pipe 6 in order to expedite passage of alkali metal vapors into the molten metal. The upper part of the bell 2' acts as a reflux condenser for the alkali metal vapors. The bell may'be submerged to any desired depth although I have found that diffusion of alkali metal vapors through the molten metal is vel'i Alkali metal is run into the bell evaporation of small amounts of alkali metal and no excess pressure is generated.

The following example is illustrative of one application of my invention:

Example 500 lbs. of molten copper is treated with sodium by the method above described, using the apparatus shown in Figure H. The sodium vapor first generated is found to be absorbed completely. After a period of a few minutes some vapor may be observed at the surface of the copper. The operation is easily controlled and introduction of alkali metal vapor into the copper takes place quietly and smoothly.

The process of my invention is applicable to the treatment of a variety of metals such as copper, iron, and others. For instance, I may treat copper with sodium to remove oxides and other impurities as described in the foregoing example. My invention is particularly valuable for this type of treatment since the alkali metal is effective in removing such impurities from copper and the prior art disclosesno' satisfacto y method for accomplishing this result. The apparatus of my invention may be constructed of any suitable material which will not contaminate the metal undergoing treatment. For instance, in the purification of copper the bell of my apparatus may be constructed of graphite since this material is comparatively inexpensive and does not introduce undesirable impurities. Parts of the apparatus not in contact with copper may be constructed of iron or of other metal which is not readily attacked by alkali metals.

means may be provided to maintain the alkali metal in the liquid state although this is generally unnecessary since'the complete operation requires only a short time and the alkali metal container may be insulated. Furthermore, it may be desirable in some cases to provide means for agitating the molten metal undergoing treatment. Inert gases other than nitrogen may be itilized to counterbalance pressure of the metal vapors and various other modifications which will be apparent to those skilled in the art may be made without departing from the scope of my invention.

It is obvious that my invention may be advantageously used for a variety of metallurgical operations. Although it is particularly valuable in the purification of metals by means of alkali metals, it is also useful in preparing the alloys of many metals with the alkali metals.

The present invention possesses many advantages over methods previously suggested for the treatment of molten metals with the low boiling alkali metals. Good contact of vapor with molten metal to be treated is obtained because of the large surface exposed around the edge of the generating bell. Residues from the vaporization of alkali metal are eliminated from the system and do not accumulate in the vaporizing chamber. Such residues circulate under the edge of the bell with the vapors and rise to the surface outside the vaporizing chamber where they are readily removed. The apparatus required is simple, inexpensive, easily replaced, and readily transported from one location to another.

The explosive hazards of the prior art methods are eliminated and my process is'easily controlled and eflicient in operation.

I claim:

1. An apparatus for the treatment of molten metals which comprises a bell. means for controlling the flow of alkali metal into the chamber of said bell, a container for alkali metal connected to said means, and pressure equalizing means connected to said container and said bell; said bell being partially submerged in molten metal.

2. An apparatus for the treatment of molten metals which comprises a vapor-confining chamber having side walls and cover, the bottom of saidchamber comprising a body of molten metal, means for admitting unvaporized alkali metal at a controlled rate into said chamber, a container for unvaporized alkali metal connected to said means, and pressure equalizing means connected to said container and said chamber.

3. An apparatus for the treatment of molten metals which comprises a vapor-confining cham ber having side walls and cover, the side walls of said chamber being of. sufficient height to provide a reflux for alkali metal vapors, the bottom of said chamber comprising a body of molten metal, means for admitting unvaporized alkali metal at a controlled rate into said chamber, and a container for unvaporized alkali metal connected to said means and means for equalizing the pressure in said chamber and said container.

4. A process for treating a molten metal bath by addition thereto of an alkali metal which comprises maintaining a body oi molten alkali metal under controlled pressure, flowing alkali metal from said body into contact with the surface of the molten metal bath to be treated so as to flash vaporize the alkali metal at such rate that there is substantially no accumulation of liquid alkali metal in contact with said metal bath, confining the resulting alkali metal vapor in contact with said bath and maintaining substantially the same pressure on said confined vapor and on the surface of said body of alkali metal. v

5. A process for treating a bath of molten copper by addition or sodium thereto which comprises maintaining a 'body of molten sodium under controlled pressure, flowing sodium from said body into contact with the surface of saidv molten copper bath so as to flash vaporize the sodium at such rate that there is substantially no; c cumulation of liquid sodium in contact with-said copper bath, confining the resulting sodium vapor in contact with said bath and maintaining substantially the same pressureon said confined vapor and on the surface of said 'body of sodium by application of an inert gas from a 5 common source.

- HARVEY N. GILBERT. 

